1. Field of the Invention
The present invention relates to an optical disc system for optically performing data writing/reading. More particularly, it relates to a light control circuit of an optical disc system which controls the level of beams emitted from a light emitting element at a predetermined rated level.
2. Description of the Related Art
An optical disc system used as a large-capacity external memory device for an information processing unit can record at a density more than ten times that of the recording density attainable by a conventional magnetic disc system.
Data recording in the optical disc system is accomplished, for example, by applying strong laser beams from a laser diode in a quantity corresponding to 5 to 10 mW as optical beams having a write power level to a recording film on an optical disc medium to form holes (pits) on the recording film by thermal reaction. This recording also can be accomplished by changing the crystal state of the recording film.
The data written in the optical recording medium can be read out from the quantity of reflected beams obtained when weak laser beams emitted from the laser diode in a quantity corresponding, for example, to about 1 mW, are applied as optical beams having a read power level to the recording film.
In order to stably obtain laser beams in quantities such as the write power level and read power. level, the emission quantity of the laser diode is monitored by a photodiode and a laser control circuit controls the emission power of the laser diode in response to the monitor current therethrough.
The laser diode has inherent characteristics, and when the laser diode is used for the optical disc system, these inherent characteristics are adjusted so that a substantially constant write power level and read power level can be obtained.
A simple control circuit is needed in which the above mentioned adjustment and control for always obtaining a constant write power level and read power level can be easily accomplished.